1. Field of the Invention
The present invention relates to a new method of conducting catalytic chemical reactions wherein separation of materials in the reaction mixture, i.e., product(s), by-product(s) or starting material(s) may be obtained by concurrent distillation or fractionation thereof.
One species of the present invention relates to the preparation of methyl tertiary butyl ether from streams containing mixtures of an isobutene and normal C.sub.4 olefin. The present invention is especially useful for the separation of isobutene from streams containing n-butenes.
2. Description of the Prior Art
Isoolefins of 4 carbon atoms are difficult to separate from the corresponding normal olefin by simple fractionation because of the closeness of their boiling points. In prior art processes as generally practiced commercially, the isoolefin is selectively absorbed by sulfuric acid and the resulting isoolefin-containing sulfuric acid extract is then diluted and heated or treated with steam to separate the isoolefin.
The n-butenes are required in pure form for homopolymerization and as feeds for the oxidative production of butadiene. One manner of separating these components is to pass the mixture through what is called a cold acid extraction procedure wherein the stream is fed into a bath of concentrated sulfuric acid. Separation is achieved by virtue of the solubility of the isobutene in the sulfuric acid, the n-butenes and other hydrocarbons present passing overhead.
Methyl tertiary butyl ether (MTBE) has gained a wide acceptance as a non environmentally harmful octane improver for gasolines. One method of separating isobutene or isoolefins in general from mixtures with the corresponding normal olefins and alkanes, has been to etherify the isoolefin with a C.sub.1 to C.sub.6 primary alcohol in the presence of an acidic cation exchange resin catalyst, separate the low boiling hydrocarbons from the higher boiling ether by fractionation, frequently followed by decomposition of the ether to recover the isoolefin. Such procedures are disclosed in U.S. Pat. Nos. 3,121,124; 3,270,081 and 3,170,000.
More recently, in view of the ether octane improving characteristics, similar processes have been disclosed for preparing and recovering the ether, e.g., U.S. Pat. Nos. 3,726,942 and 3,846,088.
In a variation on these processes disclosed in U.S. Pat. Nos. 3,629,478 and 3,634,534 to Haunschild, the mixture of isoolefin and normal olefin with lower primary alcohols is fed to distillation column in which there are a plurality of zones of acidic ion exchange resin catalyst whereby the isoolefin ether is formed and drops to the bottom of the column while the normal olefins (and paraffins) are distilled overhead. In particular, the catalyst is contained in downcomers where the reaction is to occur and the distillation takes place on the trays of the column.